Area Forecast Discussion
Issued by NWS Duluth, MN
Issued by NWS Duluth, MN
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630 FXUS63 KDLH 012344 AFDDLH Area Forecast Discussion National Weather Service Duluth MN 644 PM CDT Mon Jul 1 2024 .KEY MESSAGES... - Areas of heavy rain possible overnight into Tuesday. Flood Watch remains in effect over northern Minnesota. The potential for rain to linger into early Wednesday morning have increased. - Gusty southerly winds 30 to 40 mph possible overnight into Tuesday morning. - Another system with more heavy rain chances late Thursday through Friday. && .DISCUSSION... Issued at 302 PM CDT Mon Jul 1 2024 Through the day , a broad upper level shortwave has pushed in over the Upper Plains, along with a plume of Gulf of Mexico moisture surging northward. SPC Mesoscale Analysis shows PW values up to 1.9" along the MN/Dakotas border, expected to move eastward tonight. This saturation is present through the column, with dewpoint depressions of 1-2 degrees or less up through 500mb. Model soundings continue show a classic warm rain environment setup with freezing levels near 13kft pushing into the area overnight. This is a concerning potential heavy rain set up, on top of areas that saw 2-3x their normal June monthly rainfall. There has been some training of storms north of Grand Forks today which dropped over an inch of rain in 6 hours for some places. This convection was largely not handled well by CAMs, so have have opted to stay on the bullish side with PoPs and QPF overnight across the International Border, despite latest guidance trending the heaviest rainfall northward. A Flood Watch remains in effect across the northern third of the CWA or so, an area where soils are saturated, streamflows remain above normal, and an inch or two in a couple hours could lead to flash flooding. Some moderate to heavy rain is possible in the rest of the CWA as well overnight, with a half to one inch possible. Some over achievement of rainfall totals is possible here as well, but there is a little more room in lakes, rivers, and soils for rain to fall here, and there is less signal for possible training of storms. Overnight tonight, a screaming low level jet pushes east across the region, with 850mb wind speeds of 40-50 knots. With ongoing rain, and a weak to isothermal low level temperature modeled temperature profile, it seems reasonable that some of these winds could mix down to the surface leading to very gusty southerly winds into Tuesday morning. Some gusts of 30-40 mph could make it to the surface before this LLJ moves off and winds calm through Tuesday midday. Through the day Tuesday, a secondary shortwave embedded within a larger trough moves through, which keeps rain chances going through the day across the Northland. Scattered showers with light to moderate rain may continue into Wednesday morning. Tuesday will be a warm and very moist day with temperatures near 80 and dewpoints in the low to mid 60s. Late Thursday and into Friday, a deeper shortwave trough with a cut off low is progged to push over the International Border and sweep over the Upper Great Lakes. With good synoptic forcing and another round of attending deep moisture, this will be another one to watch for heavy rain potential. Timing has trended slightly later for the onset of this possible precipitation, now more overnight into Friday morning. Temperatures rise through the week, with high temps nearing 80 by July 4th, which is right around to slightly above normal for the time of year. && .AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/... Issued at 643 PM CDT Mon Jul 1 2024 An initial wave of precipitation is moving along and north of the Iron Range this evening, which should continue east before weakening this evening. Another wave of showers and storms should move in after 04z this evening, but have low confidence in this timing and will be making adjustments and this precipitation area, now over the central Dakotas, moves east this evening. This area of precipitation should bring deteriorating ceilings and visibilities, with a several hour period of IFR ceilings and MVFR visibilities settles into the area for the morning hours for the terminals. Some improvement to at least MVFR should occur after 18z as the precipitation moves back out of the area. Gusty southerly winds will cause very turbulent conditions through at least 15z with even stronger southerlies around 2kft of 40knots or more. && .MARINE /FOR NEAR SHORE WATERS OF WESTERN LAKE SUPERIOR/... Issued at 302 PM CDT Mon Jul 1 2024 The main concern is increasing southerly winds tonight into Tuesday ahead of an approaching low pressure system. A Small Craft Advisory is in effect for Chequamegon Bay to Saxon Harbor for late tonight into early Tuesday afternoon for gusts of 25-30 kts. Across the remainder of the South Shore to the Twin Ports, while the forecast for tonight into Tuesday favors southerly gusts just below 20 to 25 kts, strong winds aloft will be screaming at 35 to 50 knots. There is high uncertainty if these much stronger winds be able to reach the water surface and prompt an expansion of the Small Craft Advisory. There is a similar concern for Chequamegon Bay to Saxon Harbor where gale force gusts could (20-40% chance) occur. This will be closely monitored through the evening and updates will be given as needed. Should these strong winds actually manifest at the water surfaces, it will be most likely along the immediate shoreline, decreasing the further away from the mainland one gets. Some large ships may observe very strong winds at the pilot house while the surface of the lake remains largely untouched. Southerly winds should be weaker on the North Shore as those strong winds aloft are not expected to be able to make it down through the stronger stable layer there. That said, waves along the North Shore from Taconite Harbor to Grand Portage will build tonight into Tuesday to around 3-4 feet from moderate south winds in the open waters. This will be another area to watch for a Small Craft Advisory. Otherwise, widespread rain showers with embedded thunderstorms will occur overnight, decreasing through the day into Tuesday. For the open water discussion, refer to the NWS Marquette Area Forecast Discussion at weather.gov/mqt. && .DLH WATCHES/WARNINGS/ADVISORIES... MN...Flood Watch through Tuesday evening for MNZ010>012-018>021. WI...None. MARINE...Small Craft Advisory from 4 AM to 3 PM CDT Tuesday for LSZ121- 148. && $$ DISCUSSION...Levens AVIATION...LE MARINE...PA/Levens/AP